1. Field of the Invention
The present invention relates to the field of all terrain vehicles. More particularly, the invention relates to a straddle type vehicle comprising improved features.
2. Description of Prior Art
During the last decade or so, the popularity of all terrain vehicles (also referred to as xe2x80x9cATV""sxe2x80x9d) has greatly increased. These types of vehicles are indeed very practical and versatile as they may be used for work, or leisure related tasks. By virtue of their relatively compact nature, their great mobility and traction, they are capable of circulating in all sorts of surfaces, from the common back yard to the more challenging wood trail. Since they are also fairly powerful, all terrain vehicles are also used to pull or push various objects such as a trailer or a snow-plow.
Initially, these types of vehicles comprised a steerable front wheel and two driving rear wheels connected to an engine. Such three-wheeled vehicles were unstable and could overturn. In order to increase stability, the three-wheel base was therefore changed to a four-wheel base.
FIG. 1 illustrates an embodiment of a straddle type vehicle typically found in the prior art. Such a vehicle comprises four wheels mounted to a frame, the front ones being steerable. A fuel tank and a seat are disposed on an upper portion of the frame. The engine, which represents one of the heaviest components of the vehicle, is typically mounted in a central portion of the vehicle, usually below the fuel tank and a front portion of the seat. The engine location is specifically chosen to ensure a proper weight distribution. If the engine is water cooled, a radiator will be provided in front of the engine. Examples of such vehicles are described in more detail in U.S. Pat. No. 4,757,872, issued on Jul. 19, 1988, and naming Inomata as inventor and in U.S. Pat. No. 5,515,940, issued on May 14, 1996 and naming Shichinohe et al. as inventors.
While such a configuration provides vehicles with performance levels that are more than adequate, there are nonetheless many disadvantages associated with it.
In order to sit properly and drive astride, the user must xe2x80x9cmountxe2x80x9d the vehicle, i.e., he or she must raise one leg over the fuel tank, seat or rear portion of the vehicle in order to sit on or get off the vehicle. Thus, one of the main disadvantages is that access to and from the vehicle can be somewhat challenging. Because of this, some persons tend to drive while assuming a xe2x80x9cside-saddlexe2x80x9d position and changing gears using a rope tied to the gear lever. This is impractical.
Another inconvenience associated with the location of the fuel tank is that it renders engine access more difficult since there is little space between the cylinder head of the engine and the tank. This is impractical during repair since the fuel tank must be removed. Since the fuel tank is also a relatively heavy component and since it is located on the upper portion of the frame, the above-mentioned configuration also has the disadvantage of creating a relatively high center of gravity.
The location of the radiator in front of the engine also has various disadvantages. Since, during normal use, the vehicle travels mostly in the forward direction, the front-located radiator is more exposed to the possibility of being pierced by a branch or the like or being obstructed by mud. In order to compensate for this, it may be possible to cover the radiator with a protective member, but this reduces the amount of air reaching the radiator thereby reducing its cooling efficiency. This location of the radiator is also an ineffective use of valuable space. Another disadvantage of the prior art ATV shown in FIG. 1 is that the engine may be a two stroke engine, which has higher emissions levels as compared to four stroke engines. However, a four stroke engine is larger than a two stroke engine, and it therefore becomes a difficulty to adapt the ATV to accommodate a four stroke engine. The configuration referred to above also leaves very little room to accommodate storage compartments or additional accessories, especially in the front portion of the vehicle.
It is therefore an aspect of the present invention to provide a straddle-type vehicle having an improved frame and improved access features.
It is a further aspect of the present invention to provide a straddle-type vehicle having a relatively low center of gravity.
It is yet another aspect of the present invention to provide a vehicle having improved storage capabilities.
It is still another aspect of the present invention to provide an ATV having a four stroke engine that has low emissions. Even though the four stroke engine is larger than a two stroke engine, it is possible to use it while at the same time providing improved access for servicing the engine and/or for mounting the ATV.
It is yet another aspect of the present invention to provide an ATV that is arranged to allow easier mounting and dismounting therefrom.
As embodied and broadly described herein, a first preferred embodiment of the invention provides a straddle-type vehicle having a frame, a pair of front wheels suspended from a front portion of the frame, a pair of rear wheels suspended from a rear portion of the frame, a power unit mounted on the frame, a transmission allowing the power unit to transmit power to at least one of the front or rear pairs of wheels, a seat located in between the front and rear pairs of wheels, wherein a first portion of the power unit is disposed beneath the seat and a second portion of the power unit is disposed forward of the seat and below a horizontal plane defined by an uppermost portion of the seat.
In a preferred embodiment, a main portion of the transmission is also disposed beneath the seat and the power unit comprises a crankshaft and a transmission shaft extending in a running direction of the vehicle, and a rear drive shaft is connected to a rear end of the transmission shaft on one end and to a rear differential on the other end to allow the power unit to transmit power to the pair of rear wheels.
In the context of the present specification, the term xe2x80x9cdifferentialxe2x80x9d should be interpreted as meaning any type of device that is capable of imparting a rotational movement to a pair of wheels from a driving shaft, whether or not it permits one wheel to revolve faster than the other one. This includes any type of gearing such as ring and pinion gearing, spiral gearing, hypoid gearing, worm gearing or the like. This also includes any types of viscous coupling.
In another preferred embodiment, the vehicle comprises a front drive shaft connected to a front end of the transmission shaft on one end and to a front differential on the other end to allow the power unit to transmit power to the pair of front wheels.
In another embodiment the power is transmitted to at least one of the front or rear pairs of wheels through a drive chain and sprocket arrangement.
In a preferred variant, the seat is pivotably connected to the frame, the seat being moveable between a first position whereby the driver may drive the vehicle and a second position whereby the driver may access the power unit. The seat preferably comprises a pommel located at a front portion thereof and is most preferably removably connected to the frame.
Other aspects and features of the invention will become apparent by reference to the following specification and to the drawings.